1. Field of the Invention
The present invention relates to a variable compression ratio mechanism, and more particularly to a configuration to reduce a load that acts on an actuator which drives the variable compression ratio mechanism.
2. Description of Related Art
As a variable compression ratio mechanism of an internal combustion engine, the variable compression ratio mechanism in which a piston and a crank are linked through a plurality of links has been known. For example, in the related art, the piston and the crank are linked through an upper link and a lower link, and by controlling an attitude of the lower link, a compression ratio is variably controlled.
More specifically, a control link, one end of which is linked to the lower link, and the other end of which is linked to an eccentric shaft provided at a control shaft that extends substantially parallel with a crank shaft, is employed. Then, by changing a rotation angle of the control shaft (control shaft angle), the attitude of the lower link is controlled through the control link.
The control of the rotation angle of the control shaft is carried out by an actuator that is formed from a fork fixedly connected to the control shaft, an actuator rod having a ball screw shaft portion and linking to the fork through a link pin, a driving motor, a ball screw speed reducer, and a compression ratio holding mechanism to hold a set compression ratio even when an external force of a combustion pressure etc. acts.